Since liquid crystal displays are thin, light, and consume little power, they are widely used as a display for televisions, personal computers, and PDAs, for example. Particularly in recent years, upsizing of liquid crystal display devices has been rapidly progressing, as represented by liquid crystal display devices for televisions, for example. A suitable mode for an upsized liquid crystal display device is a multi-domain vertical alignment (MVA) mode which provides a wide viewing angle and allows production of a display device in high yield even if the device has a large area. Since liquid crystal molecules are aligned vertically to the substrate surfaces when a voltage is not applied to the liquid crystal layer in the multi-domain vertical alignment mode, a high contrast ratio can be achieved compared to the conventional twisted nematic (TN) mode.
In the MVA mode, the tilt direction of liquid crystal molecules is not controlled by alignment films, but is influenced by protrusions (ribs) formed from an insulating material. Therefore, an alignment treatment step for the alignment films is unnecessary, and static electricity and shavings due to factors such as rubbing are not generated, which eliminate the need for steps such as a washing step after the alignment treatment. The MVA mode leads to low diversity in initial tilts of liquid crystal molecules, and is effective in simplifying the process, improving the yield, and reducing the cost.
Still, the MVA mode requires formation of a base film corresponding to an alignment film even though it eliminates the need for an alignment treatment. Actually, the base film is also preferably eliminated in consideration of the influence of the film thickness unevenness or foreign matter contamination of the base film on the alignment of the liquid crystal molecules, and the capital investment and an increase in the number of production steps for formation of the base film.
To solve this problem, a technology for providing pretilt angles has been drawing attention which includes injecting between substrates a liquid crystal composition obtained by mixing liquid crystals with polymerizable components such as monomers or oligomers (hereinafter, also referred to as “components such as monomers”), and forming a polymer layer by polymerizing the components such as monomers while a voltage is applied between the substrates to tilt the liquid crystal molecules (for example, Patent Literatures 1 and 2). Such a polymer layer (hereinafter, also referred to as a “polymer sustained alignment (PSA) layer”) enables the liquid crystals to have a predetermined pretilt angle even after elimination of the voltage, so that the tilt direction of the liquid crystal molecules can be maintained. Here, the components such as monomers are polymerized by irradiation with heat or light (e.g., ultraviolet light).